Data interpolation is a common operation in many DSP algorithms. One target of the data interpolation is to change a signal sampling frequency. Data interpolation can also be referred to as re-sampling. Interpolation or re-sampling can be performed when a digital signal was created with a sampling frequency that is natural for that signal. For example, QAM (quadrature amplitude modulation) signals for cable or wireless communication systems can be created by sampling at twice the symbol rate frequency. After the digital signal is created, the digital signal can be transmitted with another sampling frequency, which can be defined by using a clock frequency. Typically, a communication system has a single clock frequency, while the symbol rate is programmable. A system can therefore be capable of converting data from any symbol rate to that single clock frequency. An interpolator (or re-sampler) can be used to provide the conversion.
An interpolation procedure can assume that each point of an output signal is produced on the basis of N points of an input signal, located before and after a desired output point. For example, if just two points are in use, a desired point between the two points could be calculated using linear interpolation. The desired point would belong to a direct line, connecting the two input signal points.